The present invention relates to injection molding systems and the use of an in-mold coating (IMC) in these systems, more particularly to a method for designing and producing a mold for use in connection with an injection molding system having an IMC apparatus such that articles produced by the newly designed mold can be provided with a coating.
Molded thermoplastic or thermoset articles, such as those made from polyolefins, polycarbonate, polyester, polyethylene, polypropylene, polystyrene and polyurethanes, are utilized in numerous applications including those for the automotive, marine, recreation, construction, office products, and outdoor equipment industries. Automotive industry applications include, e.g., body panels, wheel covers, bumpers, head and tail lamps, fenders, hoods, and dashboards.
When the surface quality of molded articles does not meet required standards such as those for durability, chemical resistance, and weather resistance, or to facilitate paint adhesion, such articles must be coated.
Injection molding systems are used to produce thermoplastic or thermoset articles. They allow a substrate-forming material (typically a pelletized, granular or powdered plastic material fed from a hopper) to be heated to a temperature above its melting or softening point and, using a filling pressure, injected into a closed mold maintained under a clamping pressure until the mold is substantially full; then, using a packing pressure, the mold is completely filled with the substrate-forming material to form a workpiece. The machine then maintains, under a mold or clamp pressure, the workpiece as it cools until it can be removed from the mold without distortion. (The mold typically is opened and closed either mechanically or hydraulically, usually using a predetermined timing cycle.) Such injection molding probably is the most widely used method of producing plastic parts.
Molds used in these systems generally have two parts, one of which is stationary and the other movable. The mold cavity formed by these halves generally has a first surface on one mold half upon which a show or finished surface of the molded article will be formed and a corresponding second surface on the other mold half. The stationary half typically houses the cavity section of the mold and is mounted on a stationary platen in contact with the injection section of the cylinder of the injection machine. The movable mold half typically holds the core and ejector mechanism. Injection of substrate-forming material occurs under pressure when the mold is in a closed position. The clamping pressure, i.e., the pressure used to keep the mold closed during injection of the substrate-forming material, must be greater than the pressure used to inject that material.